syms x a t h n; 
D1 = limit((sin(x)-1)/x)
D2 = limit(1/x^3,x,0,'right')
D3 = limit(1/x,x,0,'left')
D4 = limit((log(x+h)-log(x))/h,h,0)
v = [(1+a/x)^x, exp(-x)];
D5 = limit(v,x,inf,'left')
D6 = limit((1+3/n)^(4*n),n,inf)
